Coating films of graphite, or coating films of metal salts or amides of fatty acids, wax such as paraffin, etc., silicone oil, etc. have been so far formed on the surfaces of rubbery elastomers, such as gaskets made from rubber-coated metal, bearing seals, oil seals, O rings, etc. to prevent sticking and blocking, and to improve the abrasion resistance, etc., or coating films containing ethyl cellulose, phenol resin, silicone resin, or the like as a binder have been so far formed thereon. In spite of the formation of such coating films in the case of engine gaskets, etc., the rubber coating layers on the surfaces of gaskets undergo abrasion, when used under service conditions of high specific pressure, high temperatures, and further subjected to engine vibrations, sometimes resulting in gas leakage. In the case of bearing seals, oil seals, etc., the rubber coating layers at the sliding positions of rubber elastomers undergo abrasion due to repeated sliding actions, sometimes resulting in oil leakage.
In view of such a problem, the present applicant has so far proposed coating agents for rubbery elastomers capable of forming effective gaskets, etc., while maintaining a sealability, substantially free from any phenomena of abrasion or damages to the rubber coating layers on the gasket surfaces even under severe service conditions of high specific pressure, high temperatures and further under applied vibration as in the engine gasket service circumstances, that is, a coating agent for rubbery elastomers, which comprises a hydroxyl group-containing compound of liquid 1,2-polybutadiene, an isocyanate group-containing 1,2-polybutadinene as a curing agent, and a polyolefin resin (Patent Literatures 1 and 2), and also a coating agent, which comprises an isocyanate group-containing 1,2-polybutadiene resin, a wax, and a fluororesin (Patent Literature 3).
[Patent Literature 1] Japanese Patent No. 2,827,402
[Patent Literature 2] Japanese Patent No. 3,316,993
[Patent Literature 3] Japanese Patent No. 3,893,985
However, these coating agents for the rubbery elastomers have suffered from such phenomena that the polybutadiene derivative resins, one component of the coating agents, become tacky at elevated temperatures, resulting in a decrease in the friction abrasion resistance. Thus, in some cases, the coating agent layer still has a problem in the resistance at elevated temperatures.